The present invention relates to an exposed-pad Ball Grid Array (BGA) package, and more particularly, to a method of making an exposed-pad BGA package that includes die pad stamping.
A pin-grid array (PGA) and a ball-grid array (BGA) are types of microchip connection configurations that are known in the art. A PGA is a generally square chip package with a high density of pins enabling it to support a large number of input/output (I/O) from an associated microchip. The pins permit the microchip to connect to a socket or fit into solderable holes on a printed circuit board (PCB) or the like. The underside of a PGA package looks like a bed of nails. On the other hand, BGA microchips typically use a group of solder balls arranged in concentric rectangles to connect to a PCB. BGA packages often are used in applications where PGA packages would take up too much space due to the length and size of the package pins.
Referring to FIG. 1, a conventional BGA package 100 is shown. The BGA package 100 is a stacked die package that includes a first die 102 and a second die 104 attached to silicon or plastic interposer 105. The dies 102 and 104 are mechanically bonded to the interposer 105 by an epoxy or adhesive and are electrically interconnected to the interposer 105 by wires 108. The interposer 105 includes circuitry to provide electrical interconnects between the two dies 102 and 104 and to interface solder balls 110. The solder balls 110 provide electrical contacts to an external substrate, another package, test device, power source or the like. The BGA package 100 includes an encapsulant 112, which mechanically supports the package 100, allows thermal expansion and contraction, and prevents contaminants from coming into contact with the dies 102 and 104. A portion of each solder ball 110 is exposed and provides an external interface to the dies 102 and 104. The resulting overall BGA package 100 is stackable onto other BGA packages 100 or onto a PCB (not shown). Generally, the BGA package 100 is formed by coupling the semiconductor dies 102, 104 to each of the opposing faces of the interposer 105 in order to improve package space efficiency.
Another conventional BGA device 120 is shown in FIG. 2. The BGA device 120 includes a semiconductor substrate 122 such as a PCB, a flexible tape or the like. A semiconductor die 124 is mounted within the BGA device 120. Bonding pads on the surface of the semiconductor die 124 provide electrical access to the die 124. A layer 128 is applied over the surface of the substrate 122. The layer 128 may be a copper foil or an adhesive film such as a polyimide film. When the layer 128 is an adhesive film, the film is later removed and replaced with a copper foil. A mold compound 130 surrounds the die 124, bond wires 132 and a portion of the contact pads 134 of the substrate 122. Copper traces 136 are formed overlying a top surface 138 of the substrate 122. The copper traces 136 are in electrical contact with points of contact provided in the top surface 138 of the substrate 122. The bond wires 132 connect points of electrical contact in the surface of the die 124 with contact points 134 on a surface 140 of the substrate 122. The bond wires 132 are typically connected to the die 124 via ball bonds 126. Contact balls 142 are connected to contact pads 144 on the surface 140 of the substrate 122. A solder mask 146 overlays the surface 140 of the substrate 122. Openings in the solder mask 146 provide access to the contact pads 134 and 144. The contact pads 134 are for wire bond connections 132 with the die 124, and the contact pads 144 are for connections with an array of the contact balls 142.
As electronic devices become increasingly smaller and more portable, it is becoming more desirable to provide BGA devices that are thinner (i.e., have a reduced overall height or thickness) while maintaining ease and quality of manufacture. It is desirable to provide a relatively thin (BGA) type package that has a profile of less than about 0.8 millimeters (mm). It also is desirable to provide a method of forming a relatively thin exposed-pad BGA package.